Abstract: The joint of 2219-T87 aluminum alloy plate in 8 mm thickness was obtained by friction stir welding(FSW),and the microstructures and mechanical properties of the joint were investigated.The results show that the microstructure in the nugget zone(NZ) consists of refined and equiaxed grains,that in the thermal-mechanically affected zone(TMAZ) consists of deformed grains,and that in the heat-affected zone(HAZ) consists of coarse lath grains.There is an obvious interface between NZ and TMAZ at the advancing side,but there is illegibility comparatively at the retreating side.The precipitation phenomena in different zone are affected by friction stir welding.The results of tensile properties show that the transverse tensile strength of FSW joint can reach about 70% of that of the base metal.Hardness measurements show that the FSW joint is soften during welding,heat-affect zone has serious softening,and tensile specimens fracture at the HAZ of retreating side.Fractographs confirm that the fracture of the joint is the mode of ductile fracture.